Welcome to this presentation on the biology and ecology of human schistosomes. Schistosomiasis, otherwise known as bilharzia is a very important disease in the tropics, water bound disease, where you find water, fresh water. In the tropics, you will probably come across schistosoma hematoma or schistosoma mansoni. My name is Mramba Nyido. We prepared this presentation together with. We are located in the Kilimanjaro Christian America University College in Moshi, Tanzania. Welcome to the biology and ecology of human schistosomes. These schistosomes are trematodes but they are very interesting trematodes in the sense that there is a male and female schistosome. And these are the only trematodes where sexes are two, male and female. The others are hermaphroditic, which means one body will consist of the male and the female part. The free living stages need the fresh water for that development. The stages that we'll call the miracidium which comes out of the snail need to swim in fresh water in order to identify and infect a snail to develop finally into a state you call the cercaria. Which also needs to swim in fresh water to access a human host. Note that human adult schistosomes live in human blood. It is in their blood that they lay their eggs. These eggs are evacuated in feces or urine, in fresh water to ensure further development of this parasite. Take note that the poor sanitation is the problem. It perpetuates schistosomiasis. Therefore, below, we present some highlights of the biology and ecology of human schistosomes. It is our expectation that after end of the presentation, you, our participants, will appreciate that the poor sanitation is the most important phenomenon, or the most important transmission facilitation of schistosomiasis in Sub-Saharan countries. Poor sanitation perpetuates presence and the spread of human schistosomiasis. We shall show later that schistosomiasis is not a great killer. What is important is actually mortality. No, I'm contradicting myself, I'm saying that. Elsewhere, we shall show that mortality is not the issue in human schistosomiasis. The issue in human schistosomiasis is morbidity. We know that children and adolescents, and the women for that matter, are the most important culprits as far as schistosomiasis is concerned. These are groups of people, children, adolescents, and women, who, particularly in the African situation, who are more in contact with fresh water than other groups. Therefore there is a high prevalence of schistosome infection in women, in children and in adolescents. These groups, like the children, they like swimming more often than adults. Women are called upon to visit to water poison for domestic use. It is, at this point, that these groups contract human schistosomiasis. Let's look at other schistosomes. They are elongate bodies. To repeat our assess, they are the only trematodes where sexes are separate. The female is a slender worm. These female does not exist on his own. It is given the favor of being harbored by the male in an apparatus we call the gynaecophorus canal. When it is logged there, that is it's home forever. That pairing situation is important and these parasites, in that pair situation we say these parasites live in copula. So when you get, for example, schistosomiasis infection in the intestine or urinary bladder, the eggs will get to the outside through either feces or urine. They reach the exterior. They must reach fresh water to develop the embryo, which they release as the miracidium. These are some of the things that we must mention. Schistosoma hematobium, this nails bulinius, mansoni, they are Biomphalaria, japonicum, Onchomelania, mekongi, lithoglyphosis, also intercalatum is transmitted by Bulinus. It's similar to hematobium. Biomphalaria snails, intermediate hosts for Schistosoma mansoni. This is the snail. With these whiskers it's very easy to identify. We shall contrast it with what comes next. These are ice cream cone-shaped structures, the bulinus, for schistosoma hematobium. Oncomelania snails which are found in the forests of Japan and what have you, for schistosoma japonicum. Also, they like ice cream cones. Fresh water is the medium of transmission of schistosomes. Brackish water is not the medium. So we get infected by getting into contact with infected water, if you want to call it infected water, containing the infective cercariae. Morphological spine, morphology and spine of the eggs. These aid schistosome parasite speciation. You can tell whether this is hematobium, mansoni, japonicum, intercalatum, and mekongi, for that matter by looking at the egg, the spine. Schistosoma hematobium spine is elongated with a terminal spine. Mansoni is elongated with a marked lateral spine. Hematobium, terminal, this is lateral. In japonicum this is the described oval and the spine is rudimentary. And mekongi is subspherical with a minute lateral spine which I'll see the pictures as we move on. This is mansoni. This is the egg and this is the lateral spine. You cannot miss it. This is diagnostic. This is confirmatory for mansoni infection. This is terminal, spine for schistosoma hematobium. This is also diagnostic. When you come to japonicum, this is lateral spine here. This is an oval sort of body with a lateral spine, also diagnostic. Lastly, is etchola mekongi and this one is said to be subterminal sometimes slightly difficult to differentiate it from the japonicum, but that is a situation. What happens in the development of the schistosomes? In the snail miracidium develops to a sporocyst. The cercaria will consist of the head and a y-shaped tail. While in water infectivity of cercaria will diminish over time. The longer it stays, the less effective it becomes and probably 12 hours is maximum. Know to that actually, transmission is best when there's a lot of sunshine. This is when the cercaria I shared. And this is when people want to sleep. In the penetration process, the tail is shed off from the cercaria. And the cercaria will started penetrating the human skin. This is the miracidium, [BLANK AUDIO] we have talked about this very much, much earlier. This is the parasitic state that comes out of the egg, very motile. It moves very, very fast to identify the snail of interest. These are the cercariae. This is the bifurcate tail here, this is the body, and this is the head. This is a transmission electron micrograph of the same organism. When the cercarial is moving in the body it transforms into a body we call the schistosomulum. The cercarial head, as we said, reaches the dermis. The schistosomulum arises from the cercaria while in the skin. This parasite will reach the liver via the right heart and the left heart through the systemic circulation, and they find now the portal circulation system. And this will take about one week to reach the liver. Note that the male schistosomulum matures in the liver. However, the female will reach full maturity after it has paired with a male worm in the gynecophoric canal. Let's look at the adult worms. These paired adult worms in the liver move to the intrahepatic portal circulation. Where they travel to home, into the venules of the bladder in Schistosoma hematobium, or in the venules of the intestines, which will be for Schistosoma mansoni. It will detect anything from two to three months for the female worm to commence egg laying. So there are two where these other worms stay. The bladder venules and the intestinal venules depending on what parasite these species were avoid. But here you get the feeling which is psychological, that the main purpose is the eggs must be excreted to the exterior. When you are talking about a mansoni they will get into the intestine, move out through the fecal matter. When you're talking about hemotobia, they must get out with the urine to reach the environment. Now, this is the electro micrograph of shistosomes female and male in copula. The word is in copula, Latin. This is the female, which here it doesn't show, but it has been accommodated in the gynocaformicum and it lives there forever. Study question, for example, what do you consider to be the most important reason for studying the ecology and life cycle of trematode parasites? The possible answer is given there. Thank you so much for listening to this part of schistosomiasis. Thank you for your participation.
